Glulam and SCL beam
A glued laminated timber, LVL or PSL beam in bending about the strong axis, shear and bearing, to NDS 2024 Chapters 2, 3, 5 and 8 with ASCE 7-22 combinations, in ASD or LRFD. Supports, loads, combinations, shear, bearing and deflection work as in the sawn lumber beam.
Inputs of the glulam beam #
- Product: glulam (stress classes 16F-1.3E to 30F-2.1E SP and the combinations 24F-V4 and 24F-V8 DF of Supplement Table 5A), or LVL / PSL with the manufacturer's reference values (Fb at 12 in depth, Fv, Fc⊥, E, Emin) and the volume factor exponent n, CV = (12/d)^n.
- Laminating species: sets the exponent x of the glulam volume factor (x = 20 Southern Pine, 10 others). The Southern Pine stress classes require Southern Pine.
- Width b and depth d, the self-weight density, the supports and loads, the bearing length.
- Lateral stability, service conditions, deflection limits and load duration as for the sawn beam. Glulam is in wet service at 16 % moisture content or more; SCL in wet service needs the manufacturer's values.
Auto-design (editor toolbar) varies the width (standard widths) and depth (lamination increments); stress class when unlocked. Objectives: least wood (section area); shallowest, then least wood; lowest cost index. Kept unless you select them: stress class / combination. Every other input is kept; see Auto-design.
Checks performed #
| Check | Basis |
|---|---|
| Bending, positive moment | Fbx+ × (CD or KF φ λ) CM Ct × the lesser of CL and CV (NDS 5.3.6); CV by Eq. 5.3-1 with L = the span holding the peak moment (an upper bound of the distance between zero-moment points), b ≤ 10.75 in |
| Bending, negative moment | Fbx− (top face in tension) with the same factors |
| SCL bending | Fb × CL × CV, with the lesser of CL and CV when CV ≤ 1.0 and both when CV > 1.0 (NDS 8.3.6.1) |
| Beam stability CL | Eq. 3.3-6 with Ey,min (glulam, 5.2.7) or Emin (SCL); Fb* excludes CV only when CV ≤ 1.0 (3.3.3.8) |
| Beam slenderness | RB ≤ 50 (3.3.3.7) when the compression edge is unbraced |
| Shear | Fvx' (prismatic members); a note reminds that non-prismatic, notched or impact-loaded members and members at connections take Cvr = 0.72 (5.2.6, 5.3.10) |
| Bearing at the supports | Fc⊥x' with Cb (KF φ without λ in LRFD) |
| Live and total deflection | Ex (glulam) or E (SCL); creep Kcr = 1.5 dry, 2.0 wet |
Drawings #
The drawing sheet (PDF / DXF, Drawing sheet button) shows the beam elevation with the supports, the loads by type and the spans, the b × d section with the stress class (glulam laminations drawn schematically at 1 1/2 in, 1 3/8 in for Southern Pine; LVL and PSL as solid sections), and the shear, moment and deflection diagrams of the governing combinations at the elevation's scale. Camber, layup, connections, bearing hardware and brace locations are not part of the calculation; the sheet notes say so.
Limitations #
- The NDS provisions were checked against the NDS 2024 text (steps cite section and page): Eq. 5.3-1 (CV, x = 20 Southern Pine, 10 others, b ≤ 10.75 in), 5.3.6 (CV and CL not cumulative), 5.2.4 (Fbx+ / Fbx−), 5.2.7 (which E for deflection and stability), 5.1.4 (wet service at 16 %), 8.3.6.1 (SCL CV with CL), Tables 2.3.5, 2.3.6, 5.3.1, 8.3.1 and N3. Corrected: Fc⊥ takes no λ in LRFD (Table 5.3.1); for SCL with CV > 1.0, Fb* of the beam stability factor now includes CV (3.3.3.8); RB ≤ 50 is checked.
- The Supplement Table 5A values and the glulam wet service factors (Table 5A footnote) stay marked [verify]: the NDS 2024 Supplement is not on disk (
research/DOCUMENTS_NEEDED.md). SCL volume factor exponents and wet service values come from the manufacturer (NDS 8.3.3, 8.3.6). - Bending about the weak axis (y), curved and tapered members (Cc, CI), and the shear reduction Cvr are not modelled. SCL in wet service is reported as not feasible.
- The volume factor uses the span length, which is conservative for continuous beams.
Verification examples #
NDS 2024 has no worked glulam or SCL beam example. The module is verified against AWC Structural Wood Design Examples 2015/2018 Example E1.3 (published values as tabulated in the free Tekla Tedds verification example), AWC Technical Report 14 Example 3.1 (free), and hand calculations in closed form of the NDS 2024 equations (backend/tests/test_verify_glulam_beam.py). The published snow loads are ASCE 7-16 (ASD D + S); they are entered as S / 0.7 because ASCE 7-22 snow is strength level (D + 0.7S).
| Example | What it checks | Published / hand value | ILX Calcs |
|---|---|---|---|
| AWC-E1.3 | 5 × 22 24F-1.8E SP roof beam, 32 ft, purlins 1000 D + 4000 S lb at 8 ft, braced at the purlins | M = 83.8 kip-ft, RB = 11.406, Fbx+* = 2760 psi, CL = 0.978, CV = 0.951, Fb' = 2625 psi, fb = 2496 psi, V = 7918 lb, Fv' = 305 psi, fv = 108 psi, R = 12,988 lb, Fc⊥' = 650 psi, fc⊥ = 433 psi, Δ = 1.843 in | 83.8, 11.406, 2760, 0.975 (NDS 2024 uses Ey,min), 0.951, 2625, 2494, 7918, 305, 108, 12,980, 650, 433, 1.843 |
| TR14-3.1 | 2-1/2 × 21 24F-V4 ridge beam, 28 ft, D 75 + S 300 plf, braced at 4 ft | Fbx* = 2760 psi, CV = 0.9871, fb from M = 36,750 ft-lb; CL = 0.88 and M' = 37,250 ft-lb by the TR 14 buckling-moment method | 2760, 0.9871, 2400 psi; CL = 0.857, M' = 36,200 ft-lb by NDS 3.3.3 (documented deviation AWC-TR14-3.1-CL) |
| HAND-1 | 5-1/8 × 18 24F-1.8E, 24 ft, D 150 + L 400 plf | CV = 0.9475, Fb' = 2274 psi (ASD), 3928 psi (LRFD), fv at d = 92.4 psi, Δ_L = 0.666 in | same |
| HAND-2 | Same section over two 16 ft spans, L 500 plf | fb− = 693.8 psi against Fbx−' = 1430.8 psi | same |
| HAND-3 | 3-1/2 × 11-7/8 LVL, lu = 14 ft | Fb' = 2600 CL CV with CV = 1.0014 > 1.0 (both apply) | same |